In recent years, research of a light emitting apparatus which used an EL device as a self-luminous type device has been intensified, and in particular, a light emitting apparatus which used an organic material as the EL material has been attracting attention. This light emitting apparatus is also called as an organic EL display or an organic light emitting diode.
A light emitting apparatus has such a characteristic that there is no problem of a view field angle since it is of a self-luminous type, unlike a liquid crystal display apparatus. That is, as a display which is used out of doors, it is more suitable than a liquid crystal display, and uses in various forms have been proposed.
An EL device is of such a configuration that an EL layer was sandwiched between a pair of electrodes, and the EL layer is normally of a laminated configuration. Representatively, a laminated configuration of “a hole transport layer/a light emitting layer/an electron transport layer” is cited. This configuration is of very high luminous efficiency, and most of the light emitting apparatuses, for which researches and developments have been advanced at present, adopt this configuration.
The biggest problem in a practical application of an EL device is on such a point that life of the device is insufficient. Also, deterioration of the device appears in such a form that a non-luminous region (dark spot) is broadened as it is made to emit light for a long time, and as its cause, deterioration of the EL layer has become an issue.
An EL material, which forms the EL layer, is deteriorated by impurities such as oxygen and water. In addition, it is also conceivable that other impurities are included in the EL material, which has an effect on deterioration of the EL layer.
In addition, the EL material is broadly classified into a low molecular series (monomer series) material and a high molecular series (polymer series) material, and the low molecular series material among these is formed as a film, mainly by deposition. A vacuum deposition method in which a film is formed by evaporating an evaporation material from an evaporation source in vacuum is known as a representative example of a physical film forming method. In addition, as a representative example of a chemical film forming method, known is CVD (Chemical Vapor Deposition) in which a film is formed by supplying gas as material over a substrate and chemical reaction in gaseous phase or over the substrate surface.
On the occasion of carrying out film formation by a conventional deposition method, an evaporation material is used as it is, but it is conceivable that an impurity is mixed in an evaporation material at the time of deposition. That is, there is such a possibility that oxygen, water and another impurity, which is one of deterioration causes of an EL device, are mixed in.
In addition, it is possible to heighten purity by having purified an evaporation material in advance, but there is also such a possibility that an impurity is mixed in during a period until it is evaporated.
An EL material is very easily deteriorated, and it is easily oxidized and deteriorated due to existence of oxygen or water. On that account, it is impossible to carry out a photolithography process after film formation, and in order to develop a certain pattern, there is such a necessity that a mask having an opening part (hereinafter, referred to as a deposition mask) is used and it is separated at the same time as film formation. Therefore, most of the sublimed organic EL materials are attached to a deposition mask or an anti-attachment shield (a protection plate for preventing an evaporation material from being attached to an inner wall of a film forming chamber) in a film forming chamber.